If you're looking for the world's most visited tourist attraction to make a trip to, you're going to have to give more information like where you're from and which region you're looking at in particular. At least it would narrow down the choices of what people can recommend you. The top few attractions that come to mind are the Great Wall of China, Statue of Liberty, Grand Canyon, Eiffel Tower, Taj Mahal, etc. There's just so many to list from depending on what you're more keen on.